Keeping the interior of a vehicle at a comfortable temperature is important in providing driver comfort. It is desirable to maintain the interior at a comfortable temperature while the vehicle is parked. This is most notably the case for long haul truckers who sleep in the cab of the truck for the required 10-hour rest period. One way of keeping the cab of the truck cool is to maintain the engine at an idle so that the truck's regular air conditioning system can be run to cool the cab; however, this results in increased fuel consumption, pollution, engine maintenance, and most often reduces battery life. Further, exasperating the problem is that the truck's engine must be run at a higher RPM than idle to produce enough current to support sleeper loads, especially if the air conditioning system is run. If the RPM of the engine is not increased above idle, the batteries will operate in deficit.
One option is to shutdown the engine. In fact, environmental considerations have lead to federal regulations that will soon require maintaining interior cab temperatures of a Class 8 vehicle in an engine off or no-idle condition.
Thus, there exists a need for a cooling system that can keep the cab cool not only when the engine of the truck is running but also when the truck is parked and the engine is shutdown.
Referring to FIG. 1, one previously developed solution for fulfilling this need is shown. The illustrated prior art cooling system 10 includes a cold storage device 12. The cold storage device 12 is essentially a cold sink and is well known to those skilled in the art, and therefore will not be described in detail herein for the sake of brevity. While the truck engine is running, the air conditioning system 14 cools a cab 16 of the truck and turns a phase change material held within the cold storage device 12 from a liquid to a solid, i.e. freezes the phase change material. During hot days however, the conditioning system 14 does not have sufficient capacity to adequately both cool the cab 16 of the truck and cold charge the cold storage device 12, leaving the driver in a dilemma, i.e. to be comfortable while driving but not charge the cold storage device 12, making for an uncomfortable sleep, or forego cooling the cab, endure the high heat while driving, and charge the cold storage device 12 to make sleep more comfortable.
The air conditioning system 14 of FIG. 1 includes a compressor 18, a condenser 20, a receiver 22, a three-way valve 24, two expansion valves 26 and 28, and two evaporators 30 and 32. During operation, the compressor 18 compresses a refrigerant, producing a hot pressurized gas which is converted into a cool, high pressure liquid by the condenser 20. This is accomplished by passing cool ambient air by fan or other means over the condenser 20 to remove heat from the refrigerant.
The receiver 22 accumulates the liquid refrigerant produced in the condenser. The three-way valve 24 selectively directs the refrigerant to either pass through the first or the second evaporator 30 or 32 (or a selected combination thereof) via the appropriate expansion valves 26 and/or 28. The expansion valves 26 and 28 transform the high pressure liquid refrigerant to a low temperature, low pressure gas and/or liquid mixture refrigerant.
The first evaporator 30 is located in heat exchange communication with the cab 16. A fan 34 is used to pass air over the first evaporator 30, which cools the air, which is then directed into the cab to cool the same. The second evaporator 32 is located in the cold storage device 12 and is used to cool the phase change material present therein, preferably converting the phase change material to a solid.
When the truck engine is shutdown, the engine driven compressor 18 cannot be run as it is driven by the engine. Further, even if one were to attempt to drive the compressor by using an electric motor utilizing power obtained from the truck's batteries, the current draw required to drive a compressor of the size required to draw down the entire cab would drain the batteries in such a short period that such an arrangement is unfeasible. For instance, a typical compressor of the size required to draw down the entire cab typically requires approximately 8 horsepower to run at full capacity, which, on a 12-volt system, would draw 200 amps. Such a large draw would drain a truck battery in a very short period.
Thus, in previously developed cooling systems, if cab cooling is desired with the engine shutdown, a heat transfer system 35 is used. The heat transfer system 35 uses an electric pump 36. The electric pump 36 pumps antifreeze infused water through heat exchange coils 38 embedded in the cold storage device 12, thereby reducing the temperature of the antifreeze infused water and partially melting the phase change material contained in the cold storage device 12. The cooled antifreeze infused water then passes through a heat exchanger 40. An electric fan 42 blows air over the coils of the heat exchanger 40, thereby blowing cold air into the cab 16 to cool the cab 16.
Although effective, this previously developed cooling system 10 is not without its problems. First, the standard truck air conditioning system 14 is required to produce 38–42° F. air at a cabin diffuser while the thermal storage unit is required to support temperatures in the 26° F. range. Therefore, the truck air conditioning system must cycle off for a short time while the storage system switches the compressor to a higher pressure mode to produce 26° F. temperatures for use in the thermal storage unit. Typically, when the ambient temperatures are in excess of 100° F., the standard engine air conditioning system is not adequate and often becomes overloaded attempting to cool the cab 16 and convert the phase change material of the cold storage device 12 to a solid. Further, with the engine shutdown, the cold storage device 12 cannot be recharged; thus the ability to cool the cab 16 is limited to the cooling capacity of the cold storage device 12 at time of engine shut-down. Thus, there exists a need for a vehicle cooling system that reduces the load on the truck's regular air conditioning system so it does not become overloaded attempting to cool both the cab of the truck and the cold storage device. Further, there exists a need for a vehicle cooling system that is operable to recharge the cold storage device even when the engine of the vehicle is shutdown and plugged into shore power, i.e. plugged into an alternating current power source provided to mobile users at places such as truck stops, parking lots, warehouses, loading docks, driver's home, etc.